On-demand electro-hydraulic steering system

ABSTRACT

A method of steering a vehicle with a hydraulic steering system is disclosed. A first control signal is sent to a pilot valve. The pilot valve is operated to direct pilot fluid to a main valve in response to the first control signal. The main valve is opened to a first position in response to the pilot fluid. Fluid is directed through the main valve to a first actuator. Resistance to actuation of the first actuator is detected. The detected resistance is compared to a threshold resistance. A second control signal is sent to the pilot valve when the detected resistance exceeds the threshold resistance. The pilot valve is operated to direct pilot fluid to the main valve in response to the second control signal. The main valve is opened to a second position in response to the pilot fluid. Fluid is directed through the main valve to the first actuator and a second actuator.

This a division of application Ser. No. 11/094,291, filed Mar. 31, 2005,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This disclosure is directed generally to an electro-hydraulic steeringsystem and, more particularly, this disclosure is directed to anon-demand electro-hydraulic steering system for a work machine.

BACKGROUND

Earthmoving and construction work machines often employ hydraulicsteering systems that control steering functions and operation. Thesesteering systems often provide pressurized fluid to hydraulic actuatorsarranged to change a steering angle of front or rear wheels to steer thework machine.

On a conventional work machine, a steering system includes two steeringactuators that control the steering angle of the wheels. Duringsteering, the system typically extends one actuator while retracting theother. Extending and retracting the actuators often may be accomplishedby introducing pressurized fluid into a head end of one actuator and arod end of the other actuator. Thus, both actuators provide a steeringforce to change the wheel steering angle and steer the work machine.

One example of a known system that provides conventional steeringcontrol is disclosed in U.S. Pat. No. 5,520,262. The system includes athree position directional valve disposed between a pump and a pair ofsteering cylinders. The valve and fluid lines are arranged to providefluid to both steering cylinders to implement either a right or leftturn. Accordingly, when turning, fluid is fed to the head end of onesteering cylinder and the rod end of the other steering cylinder.

While the system disclosed in the '262 patent may be effective forproviding steering control, the system may also introduce someinefficiencies. These efficiencies may occur because, in addition tohydraulic steering control, a conventional work machine includes manyadditional systems and implements requiring hydraulic power. Forexample, work machines, such as wheel loaders, may include a loadingbucket moveable with hydraulic powered actuators. While steering,conventional steering systems may draw fluid away from these additionalhydraulically powered systems and implements, thereby reducing the fluidpower available to those systems and implements.

In addition, conventional steering control systems may provide moresteering force than is necessary, thereby resulting in additionalinefficiencies. For example, one or more hydraulic pumps may generatethe fluid pressure used for steering. These pumps may be driven by anengine, such as an internal combustion engine. Therefore, operating thepumps to provide more fluid pressure than may be required may increasethe load on the engine, and likewise, increase fuel consumption.

Another known hydraulic system that may allow implement control whilesteering may be configured to provide fluid power to only one of twosteering actuators, thereby maintaining fluid and fluid power foroperation of the other implements. If the fluid power at the poweredactuator is insufficient to properly steer the work machine, thesteering system may direct fluid to both actuators. However, the knownsystem is complex, includes many components, and may be difficult toimplement. For example, the system does not use a main valve thatcontrols flow to all the chambers. The many components necessary tooperate the known steering system may increase production costs and mayreduce reliability.

Yet another system that provides fluid power first, to only one of twosteering actuators, and then if required, to a second steering actuatoris disclosed in U.S. Pat. No. 5,193,637. The '637 patent discloses asystem that uses a control valve that connects one chamber of a firststeering piston cylinder to a fluid pump. A directional valve is used todirect fluid to a chamber of a second steering piston cylinder whenfluid pressure exceeds a given amount. The system disclosed in the '637patent requires multiple valves in communication with the steeringpiston cylinders and, therefore, may be overly complex and expensive.

What is needed is a steering system that may be less complex, lessexpensive, more efficient, and more compact than previous steeringsystems, yet still may provide desired pressure during steering toadditional hydraulic systems and implements. The system disclosed anddescribed herein may overcome one or more of the problems in the priorart.

SUMMARY

In one exemplary aspect, a method of steering a vehicle with a hydraulicsteering system is disclosed. The method may include sending a firstcontrol signal to a pilot valve. The pilot valve may be operated todirect pilot fluid to a main valve in response to the first controlsignal. The main valve may be opened to a first position in response tothe pilot fluid. Fluid may be directed through the main valve to a firstactuator. Resistance to actuation of the first actuator may be detected.The detected resistance may be compared to a threshold resistance. Themethod may include sending a second control signal to the pilot valvewhen the detected resistance exceeds the threshold resistance. The pilotvalve may be operated to direct pilot fluid to the main valve inresponse to the second control signal. The main valve may be opened to asecond position in response to the pilot fluid. Fluid may be directedthrough the main valve to the first actuator and a second actuator.

In another exemplary aspect, a method of operating the hydraulicsteering system of a machine is disclosed. The method may includesending a first control signal from a control module to a pilot valve.The pilot valve may be operated to direct pilot fluid to a nine-way,five-position pilot operated directional spool valve in response to thefirst control signal. The nine-way, five-position pilot operateddirectional spool valve may be opened to a low pressure position inresponse to the pilot fluid. Fluid may be directed through the nine-way,five-position pilot operated directional spool valve to a head portionof a first actuator. Resistance to actuation of the first actuator maybe detected. The detected resistance may be compared to a thresholdresistance with the control module. The method also may include sendinga second control signal from the control module to the pilot valve whenthe detected resistance exceeds the threshold resistance. The pilotvalve may be operated to direct pilot fluid to the nine-way,five-position pilot operated directional spool valve in response to thesecond control signal. The nine-way, five-position pilot operateddirectional spool valve may be opened to a high pressure position inresponse to the pilot fluid. Fluid may be directed through the nine-way,five-position pilot operated directional spool valve to the head portionof the first actuator and a rod portion of a second actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary work machine;

FIG. 2 is a schematic representation of an exemplary electro-hydraulicsteering system; and

FIG. 3 is a schematic representation of an exemplary electrical controlsystem for the electro-hydraulic steering system in FIG. 2.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments that areillustrated in the accompanying drawings. Wherever possible, the samereference numbers will be used throughout the drawings to refer to thesame or like parts. While specific configurations and arrangements arediscussed, it should be understood that this is done for illustrativepurposes only.

FIG. 1 shows an exemplary work machine 100 that may incorporate anelectro-hydraulic steering system as disclosed herein. The work machine100 may include an engine housing 102, an operator station 104, and awork implement 106, such as, for example, a bucket for digging andloading material. In the example of work machine 100 being a wheelloader, the work implement 106 is powered and controlled by a number ofactuators, including a tilt actuator 108.

The work machine 100 may include front and rear ground engaging devices,such as front wheels 110 and rear wheels 112 that support the workmachine 100. The engine housing 102 may include a power source, such asan engine 114, that may provide power to the front and/or rear wheels110, 112.

To drive the work machine 100, an operator may manipulate one or moresteering input devices that may be housed within the operator station104. The input devices may ultimately steer the work machine 100 byextending and retracting hydraulic steering actuators (not shown in FIG.1). In the example of work machine 100 being a wheel loader, the workmachine 100 may include a front end 116 and a back end 118. Thehydraulic steering actuators may extend between the front and back ends116, 118 and may be configured to articulate the front end 116 relativeto the back end 118 about an articulation axis 120. Although theelectro-hydraulic steering system is discussed with reference to anarticulating work machine, the principles and system described hereinare equally applicable to a more conventional hydraulic steering systemthat may turn the wheels relative to the work machine body to steer thework machine.

FIG. 2 illustrates an exemplary electro-hydraulic system 200 that may beincorporated on the work machine 100 to provide steering control. Theelectro-hydraulic system may include first and second steering actuators202, 204 that provide the steering control. The electro-hydraulic system200 also may include a plurality of fluid components and electricalcomponents that cooperate together to control the extension andretraction of the steering actuators 202, 204, to thereby steer the workmachine 100. For purposes of clarity, the steering actuators will bedescribed first, followed by a description of the fluid components, andthen by a description of the electrical components.

The first and second steering actuators 202, 204 may be actuators knownin the art, and may be, for example, hydraulic driven cylinders. Thefirst and second steering actuators 202, 204 may include first andsecond tubes 206, 208, respectively, and first and second pistonassemblies 210, 212, respectively. The first piston assembly 210 dividesthe first tube 206 into a first and a second chamber 214, 216, and thesecond piston assembly 212 divides the second tube 208 into a third anda fourth chamber 218, 220. The chambers 214, 216, 218, 220 of eachsteering actuator 202, 204 may be selectively supplied with apressurized fluid and drained of the pressurized fluid to cause thepiston assemblies 210, 212 to displace within the tubes 206, 208,thereby changing the effective length of the steering actuators 202,204. Because the piston assemblies 210, 212 include a rod at one side,the effective area of the piston assemblies 210, 212 adjacent the firstand third chambers 214, 218, i.e., the head portions of the steeringactuators, is greater than the effective area of the piston assemblies210, 212 adjacent the second and fourth chambers 216, 220, i.e., the rodportions of the steering actuators.

The expansion and retraction of the steering actuators 202, 204 mayfunction to control the steering of the work machine 100. To provideuniform force for either a right or a left turn, the steering actuators202, 204 may be configured on the work machine 100 in a manner thatextension of one of the steering actuators 202, 204 results in theretraction of the other. In the exemplary embodiment of the articulatedwheel loader shown in FIG. 1, the first and second steering actuators202, 204 may extend between the front and back ends 116, 118 in FIG. 1,with the first actuator 202 being configured to extend to turn the workmachine 100 to the right while the second actuator 204 retracts.Similarly, a left turn would require that the second actuator 204 extendwhile the first actuator 202 retracts. Either the first or secondactuators 202, 204 could be arranged to extend to effect either a rightor a left turn. Other configurations may also be used, as may be thecase on a non-articulating vehicle.

The fluid components may include a tank 222, a primary steering system224, a redundant steering system 226, an on-off valve 228, a main valve230, and right and left shuttle valves 232, 234. In addition, the fluidcomponents may include additional features, including, for example,cross-over relief and make-up valves 236, one or more back pressurevalves 238, and a pressure compensator valve 240. It is contemplatedthat electro-hydraulic system 200 may include additional and/ordifferent components than those shown such as, for example,accumulators, restrictive orifices, check valves, pressure reliefvalves, makeup valves, pressure-balancing passageways, and othercomponents known in the art. It is contemplated that other componentsmay also be utilized in the system to customize the system according tospecific needs.

The tank 222 may constitute a reservoir configured to hold a supply offluid, such as, for example, a dedicated hydraulic oil, an enginelubrication oil, a transmission lubrication oil, or any other fluidknown in the art. Besides the electro-hydraulic system 200, one or moreadditional hydraulic systems within the work machine 100 may draw fluidfrom and return fluid to the tank 222. It is also contemplated that theelectro-hydraulic system 200 may be connected to multiple separate fluidtanks.

The primary and redundant steering systems 224, 226 may be configured toprovide fluid from the tank 222 to the main valve 230. The primarysteering system 224 may include a fluid source such as a first fluidsource 242 and/or a second fluid source 250, a right primary steeringpilot valve 244, a left primary steering pilot valve 246, and a primarypressure reducing valve 248. Similarly, the redundant steering system226 may include a fluid source such as at least one of the first orsecond fluid sources 242, 250, a right redundant steering pilot valve252, a left redundant steering pilot valve 254, and a redundant pressurereducing valve 256.

The first and second fluid sources 242, 250 may be configured to eachdraw fluid from the tank 222 and produce a flow of pressurized fluid tothe steering pilot valves 244, 246, 252, 254, the main valve 230, andthe steering actuators 202, 204. The first and second fluid sources 242,250 may each constitute, for example, a variable displacement pump, afixed displacement pump, a variable delivery pump, or any otherpressurizing system known in the art. The first and second fluid sources242, 250 may be drivably connected to a power source, such as the engine114 in FIG. 1, by for example, a countershaft (not shown), a belt (notshown), an electrical circuit (not shown), or in any other suitablemanner. Alternatively, the first fluid source 242 may be indirectlyconnected to the power source, such as the engine 114, via a torqueconverter, a gear box, or in any other appropriate manner. The secondfluid source 250 may be ground driven through a transmission transfergear, and may be a secondary steering pump. It is contemplated thatmultiple sources of pressurized fluid may be interconnected to supplypressurized fluid to electro-hydraulic system 200.

The right and left primary steering pilot valves 244, 246 and the rightand left redundant steering pilot valves 252, 254 may be 3-way,2-position proportional solenoid reducing valves in fluid communicationwith the first and second fluid sources 242, 250. The steering pilotvalves 244, 246, 252, 254 may be independently controlled and configuredto direct pilot fluid to the main valve 230. In so doing, the pilotfluid from the steering pilot valves 244, 246, 252, 254 may affect theamount of fluid flow through the main valve 230, thereby ultimatelycontrolling the rate and direction of extension of the first and secondsteering actuators 202, 204. In one exemplary embodiment, the right andleft primary steering pilot valves 244, 246 comprise the two separatevalves as shown in FIG. 2. In another exemplary embodiment, the rightand left primary steering pilot valves 244, 246 may comprise a singlevalve, such as, for example, a 4-way, 3-position valve. Likewise, theright and left redundant steering pilot valves 252, 254 also maycomprise two separate valves as shown, or a single valve. Other valveconfigurations for the valves 244, 246, 252, and 254 also would beapparent to one skilled in the art.

The primary pressure reducing valve 248 and the redundant pressurereducing valve 256 are operable in a known manner and are configured toreduce the fluid pressure fed from the first and second fluid sources242, 250 to the respective primary and redundant steering pilot valves244, 246, 252, 254.

The on-off valve 228 may be a solenoid operated valve operable tocontrol fluid flow to the primary system. In the exemplary embodimentshown, the on-off valve 228 is disposed between the primary pressurereducing valve 248 and the left and right primary valves 244, 246. Whenthe on-off valve 228 is OFF, fluid may be allowed to flow to the leftand right primary steering pilot valves 244, 246, and when the on-offvalve 228 is ON, fluid may not be allowed to flow to the primarysteering pilot valves 244, 246. Accordingly, when the on-off valve 228is ON, the primary steering system 224 may not be capable of controllingthe position of the main valve 230 and, therefore, may not control thesteering of the work machine 100.

The main valve 230 may be in fluid communication with the first andsecond fluid sources 242, 250 and may be configured to regulate theamount of fluid passed to the steering actuators 202, 204 to effectactuation and any desired steering adjustment. In addition, the mainvalve 230 may be a pilot operated valve in fluid communication with theprimary and redundant steering pilot valves 244, 246, 252, 254.Accordingly, pilot fluid from the steering pilot valves 244, 246, 252,254 may directly affect the position of the main valve 230, whichdirectly affects the amount of fluid allowed to flow to the steeringactuators 202, 204. In the example shown, the main valve 230 is a 9-way,5-position pilot operated directional spool valve operable to controlthe flow of pressurized fluid to each of the steering actuators 202,204. Based upon the five positions, fluid is directed to the steeringactuators 202, 204 at different directions and rates, thereby providingthe steering control. In addition to being a spool valve, in otherexemplary embodiments, the main valve 230 may be a rotary valve or othertype of multi-position valve.

In the exemplary embodiment shown, the five positions include a lefthigh power position 258, a left low power position 260, a no-flowposition 262, a right low power position 264, and a right high powerposition 266. The left high power position 258 is configured to directfluid flow to the second and third chambers 216, 218 of the first andsecond actuators 202, 204, while the first and fourth chambers 214, 220are allowed to drain to the tank 222. The left low power position 260may be configured to direct fluid flow to only the third chamber 218,while the first, second, and fourth chambers 214, 216, 220 are allowedto drain to the tank 222. The no-flow position 262 may be configured toeffectively block flow to both steering actuators 202, 204. The rightlow power position 264 is configured to direct fluid flow to the firstchamber 214, while the second, third, and fourth chambers 216, 218, 220are open to the tank 222. The right high power position 266 isconfigured to direct fluid flow to the first and fourth chambers 214,220, while the second and third chambers 216, 218 are open to the tank222. Springs at each end of the main valve 230 bias the main valve 230to the no-flow position 262.

The right shuttle valve 232 is operable to selectively direct fluid flowfrom one of the right primary steering pilot valve 244 and the rightredundant steering pilot valve 252 to the main valve 230 to shift theposition of the main valve 230. Likewise, the left shuttle valve 234 isoperable to selectively direct fluid flow from one of the left primarysteering pilot valve 246 and the left redundant steering pilot valve 254to the main valve 230 to shift the position of the main valve 230.Therefore, the shuttle valves 232, 234 may be operable to selectivelydirect fluid from one of the primary and the redundant steering systems224, 226 to control the position of the main valve 230 and therebycontrol the amount of fluid from the main valve 230 to the steeringactuators 202, 204.

The cross-over relief and make-up valves 236 may be associated with thefluid lines between the main valve 230 and the steering actuators 202,204. The cross-over relief and make-up valves 236 may provide shockrelief in a manner known in the art. The cross-over relief and make-upvalves 236 may include two types of valves, with the cross-over reliefvalves being configured to absorb pressure spikes and the make-up valvesbeing configured to prevent the steering cylinder from voiding byproviding oil flow and pressure from the return line to steeringcylinder. The back-pressure valve 238 may be disposed in a return linefrom the steering actuators 202, 204 and may be configured to maintain alevel of pressure in the steering actuators 202, 204 to enhanceresponsiveness. The pressure compensator valve 240 may be an optionalvalve that may be included when the fluid pressure from the first andsecond fluid sources 242, 250 is used to provide fluid power managementto additional components on the work machine 100. Accordingly, in oneexemplary embodiment, when the electro-hydraulic steering system 200 iscombined with a second circuit, then the pressure compensator valve 240may help to provide a flow sharing feature that will be used as back-upto provide electronic priority or hydro-mechanical priority to thesteering system 200 over the second circuit. The pressure compensatorvalve 240 may be configured to ensure that although fluid may be used tocontrol other components, a sufficient amount of fluid is alwaysavailable for the electro-hydraulic steering system 200.

The electrical components of the electro-hydraulic system 200 aredescribed with reference to FIGS. 2 and 3. The electrical components mayform a control system 300 that may include pressure sensors (shown inFIGS. 2 and 3), an input device 302, an input sensor 304, and a controlmodule 306 (all shown in FIG. 3). The pressure sensors may be associatedwith the fluid lines between components or with the componentsthemselves and may monitor fluid pressures within the electro-hydraulicsystem 200. In this embodiment, the pressure sensors may include a firstpressure sensor 308 and a second pressure sensor 310 associated with thefirst and second actuators 202, 204, respectively. Additional pressuresensors may include a right pressure sensor 312, a left pressure sensor314, and a main line pressure sensor 316. In the exemplary embodimentshown, the first and second pressure sensors 308, 310 may each beconfigured to respectively monitor the pressure associated with thefirst chamber 214 of the first actuator 202 and the third chamber 218 ofthe second actuator 204. In one exemplary embodiment, the first andsecond pressure sensors 308, 310 may be disposed within a head portionof the steering actuators 202, 204. However, the first and secondpressure sensors 308, 310 instead may be disposed to monitor thepressure in the fluid lines between the first and third chambers 214,218 and the main valve 230.

Although the electro-hydraulic system 200 employs pressure sensors 308,310 to measure the fluid pressure, the sensors could be any sensorsconfigured to monitor parameters indicative of resistance to actuationof the first and second actuators 202, 204. Resistance to actuation maybe an indication of resistance to turning at the wheels 110, 112 of thework machine 100. In one exemplary embodiment, resistance to actuationmay be detected by monitoring the articulation rate of the work machineor of the wheels by sensors. The detected rate then may be compared torate values stored in the control module 306. In another exemplaryembodiment, the resistance to actuation may be based on a monitoredvelocity or position. Again, the monitored velocity or position may becompared to threshold velocities or positions stored within the controlmodule 306. As used herein, the term “detecting resistance to steeringactuation” may be inclusive of any parameter that may be monitored todetect resistance to a turn.

In use, an output from any of the pressure sensors 308, 310, 312, 314,316 (or any sensor that detects resistance to actuation) may becommunicated as an input to the control module 306, which in response,may increase current (the command) to the relevant proportional solenoidsteering pilot valves 244, 246, 252, 254. In turn, this may increase thepilot signal to one side of the main valve 230, thereby further shiftingthe main valve 230 to either the left or right high power positions 258,266. In one exemplary embodiment, the pressure sensors 308, 310 may bereplaced by a single optional pressure sensor (labeled LS in FIG. 2)that may be installed in communication with the main valve 230 and maymeasure only the load sensing signal. This would allow proper operationwhile employing fewer sensors than in the exemplary embodiment shown.

As shown in FIG. 2, the right and left pressure sensors 312, 314 may bedisposed in a manner to monitor pressure between the main valve 230 andthe respective right and left shuttle valves 232, 234. By monitoring thefluid pressure between the shuttle valves 232, 234 and the main valve230, the right and left pressure sensors 312, 314 may detect the pilotforce being applied to shift the main valve 230 to control the steeringon the work machine 100. The main line pressure sensor 316 may beconfigured to monitor the fluid pressure being fed to the right and leftprimary steering pilot valves 244, 246. In the exemplary embodimentshown in FIG. 2, the main line pressure sensor 316 is disposed betweenthe primary pressure reducing valve 248 and the on-off valve 228. Thepressure sensors 312, 314, 316 may be disposed at other locations aboutthe electro-hydraulic system 200 to provide desired data about thesystem's operating condition.

The input device 302 could be a rotary device such as a steering wheel,linear device such as a joystick, or other input device known in theart, and may be disposed within the operator station 104 formanipulation by a work machine operator. Configured to generate adesired movement signal, the input device 302 sends input to the controlmodule 306 as an electrical steering signal. For example, in theexemplary embodiment where the input device 302 is a steering wheel, anoperator may turn the steering wheel to generate a steering signal as acommand to operate the electro-hydraulic system 200 to effect thedesired turn. An optional sensor 304, such as a transducer, may beassociated with the input device 302 and may be used to detectmanipulation of the input device 302. Thus, the sensor 304 may generatethe steering signal.

The control module 306 may include a processor and memory. The memorymay store one or more routines executable by the processor, which couldbe software programs, for controlling the electro-hydraulic system 200.In addition, the memory may store pre-established threshold values usedto determine when resistance to a turn is excessive. The control module306 may use the stored threshold values to distinguish when turning thework machine may be satisfactorily accomplished with a low power turnand when turning the work machine may be more satisfactorilyaccomplished with a high power turn.

The control module 306 may be operable to receive data indicative of adesired steering direction from the input device 302 or sensor 304 andindicative of fluid pressure from one or more of the pressure sensors308, 310, 312, 314, 316. Based upon the data received, the controlmodule 306 may control any of the solenoid actuated valves of theelectro-hydraulic system 200, such as the steering pilot valves 244,246, 252, 254 and the on-off solenoid valve 228. The control module 306may be configured to generate a control signal based on the input signalfrom the input device 302 and control the solenoid actuated valves 244,246, 252, 254, 228 to provide an appropriate signal to affect the mainvalve 230, thereby controlling the steering of the work machine 100.

In one exemplary embodiment, the control module 306 may be configured tocontrol the steering pilot valves to provide pilot pressure to move themain valve 230 to one of the five steering positions 258, 260, 262, 264,266. For example, upon receipt of a steering signal from the inputdevice 302, the control module 306 may operate the steering pilot valvesto provide pilot fluid to position the main valve 230 to the left lowpower position 260. If the pressure in the third chamber 218, asdetected by the second pressure sensor 310, increases beyond apre-established amount, the control module 306 may further operate thesteering pilot valves to provide pilot fluid to position the main valve230 at the left high power position 258. By shifting the main valve 230,the additional power is used to provide turning force at the steeringactuators 202, 204.

In one alternative embodiment, the electro-hydraulic steering system 200may be configured in a manner to direct the fluid to the second andfourth chambers in the low power positions, rather than the first andthird chambers. In such an embodiment, the electro-hydraulic system maycollect data indicative of resistance to a turn by, for example,monitoring the pressure at the second and fourth chambers. As explainedabove, other methods may be used to monitor resistance to a turn.

INDUSTRIAL APPLICABILITY

The electro-hydraulic steering system 200 described herein may reducethe amount of pressurized fluid used to steer the work machine 100during many operating scenarios, thereby increasing the amount ofpressurized fluid that is available, while steering, for the operationof other, non-steering systems and implements. This may enable the workmachine 100 to operate the non-steering systems and implements during aturn with a minimized pressure loss, thereby enhancing responsivenessand control of the non-steering implements. Accordingly, the workmachine 100 may be able to operate more efficiently as it continues toperform other functions at satisfactory rates. In addition, because thework machine 100 may be capable of providing satisfactory fluid powermanagement to both the steering system and the non-steering systems, theengine 114 and other components that drive the fluid sources 242, 250,may be operated at lower speeds while still providing the same work orenergy. This may reduce fuel costs, resulting in efficiencies in fuelconsumption.

In addition, the electro-hydraulic system 200 described herein may becost-effective by providing control through a main valve, such as themain valve 230, as opposed to multiple valves. Combining functions ofmultiple valves into a main valve may provide efficient use of space onthe work machine 100 and may reduce overall manufacturing costs.

The electro-hydraulic steering system 200 may operate by supplying afirst amount of pressurized fluid to the steering actuators 202, 204during a turn. If the steering is not as responsive as desired, a secondamount of pressurized fluid may be directed to the steering actuators202, 204 to provide additional steering power. Accordingly, steeringoperates at low power unless low power is not sufficient, then thesteering operates at high power. One exemplary description of a steeringmethod is described below.

An operator may desire to implement a turn on the work machine 100 bymanipulating the input device 302. The input device 302 may send asteering signal to the control module 306 or, alternatively, the sensor304 may send a steering signal to the control module 306 indicative ofthe operator's desire. The control module 306 may receive the steeringsignal and generate a steering command signal.

The steering signal may be an instructive signal to open one of thesolenoid driven steering pilot valves 244, 246, 252, 254 a desiredamount. The steering command signal may be communicated to theappropriate steering pilot valve 244, 246, 252, 254, and the steeringpilot valve may operate to provide pilot fluid that controls theposition of the main valve 230. Initially, the steering pilot valves244, 246, 252, 254 may provide pilot fluid to move the main valve 230 toa low power position, such as the right or left low power positions 260,264. At the low power position, fluid may be directed to one of the fourchambers 214, 216, 218, 220 in the steering actuators 202, 204, whilethe other three chambers are open to the tank.

During this time, the draw of pressurized fluid is limited to one of thefour chambers 214, 216, 218, 220 of the steering actuators 202, 204,providing the remainder of the pressurized fluid for operation of other,non-steering implements on the work machine 100. For example, eventhough the steering system is drawing fluid to execute a turn, the workimplement 106 may be controlled with minimal loss of fluid power.

As the piston assemblies 210, 212 within the steering actuators 202, 204move in response to the low power fluid, the pressure sensors 308, 310monitor fluid pressure at the chamber being filled and communicatesignals indicative of the monitored fluid pressures to the controlmodule 306. The control module 306 may have stored therein a series ofpre-established threshold pressure values for each input from the inputdevice 302. If the monitored pressure is above the pre-establishedthreshold value, then the control module 306 may determine that thesteering system is encountering resistance to the turn. Resistance couldbe caused by a number of exterior factors, including the type of terrainbeing traversed, such as sand or rock, the wetness of the ground, suchas muddy or dry, and other environmental factors.

If the control module 306 determines that the fluid is above thethreshold value, then the control module 306 may increase the turningpower of the steering system. This may be accomplished when the controlmodule 306 sends a revised steering command signal to the appropriatesteering pilot valve to further open the steering pilot valve toincrease the pilot fluid pressure. In response to the increased pilotpressure, the main valve 320 may shift positions from the left or rightlow power position 260, 264 to the left or right high power position258, 266. Doing so provides pressurized fluid flow to two chambers ofthe steering actuators 202, 204 instead of one. Accordingly, thesteering system provides higher forces, thereby ensuring that thesteering system is sufficiently responsive.

In one exemplary embodiment, once the fluid pressure, as detected by thefirst or second pressure sensors 308, 310 falls below the thresholdvalue, the control module 306 may change the control signal to thesteering pilot valve to reduce the pilot pressure at the main valve 230,thereby allowing the main valve 230 to again be positioned at the lowpower position.

Although the electro-hydraulic steering system 200 is discussed withreference to an articulating work machine, the principles and systemdescribed herein are equally applicable to a more conventional hydraulicsteering system that may turn the wheels relative to the work machinebody to steer the work machine.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the disclosed embodimentswithout departing from the scope of the disclosure. Other embodimentswill be apparent to those skilled in the art from consideration of thespecification and practice of the embodiments disclosed herein. It isintended that the specification and examples be considered as exemplaryonly, with a true scope of the disclosure being indicated by thefollowing claims.

1. A method of steering a vehicle with a hydraulic steering system,comprising: sending a first control signal to a pilot valve; operatingthe pilot valve to direct pilot fluid to a main valve in response to thefirst control signal; opening the main valve to a first position inresponse to the pilot fluid; directing fluid through the main valve to afirst actuator; detecting resistance to actuation of the first actuator;comparing the detected resistance to a threshold resistance; sending asecond control signal to the pilot valve when the detected resistanceexceeds the threshold resistance; operating the pilot valve to directpilot fluid to the main valve in response to the second control signal;opening the main valve to a second position in response to the pilotfluid; and directing fluid through the main valve to the first actuatorand a second actuator.
 2. The method of claim 1, including receiving asteering signal at an input device, the first control signal being sentin response to the steering signal.
 3. The method of claim 1, whereindetecting resistance to actuation includes one of monitoring a fluidpressure and monitoring a turn rate.
 4. The method of claim 3, whereinmonitoring a fluid pressure includes monitoring the fluid pressure witha pressure sensor disposed within a head portion of the first and secondactuators.
 5. The method of claim 3, wherein monitoring a fluid pressureincludes monitoring the fluid pressure between the main valve and thefirst and second actuators.
 6. The method of claim 1, wherein directingfluid through the main valve to the first actuator and the secondactuator includes directing fluid to extend the first actuator andretract the second actuator.
 7. The method of claim 1, wherein the pilotvalve is a solenoid operated valve and sending the first control to thepilot valve includes sending an electrical signal to activate thesolenoid.
 8. The method of claim 1, wherein directing fluid through themain valve to a first actuator and directing fluid through the mainvalve to the first actuator and the second actuator include directingfluid through a multi-position directional valve.
 9. The method of claim8, wherein directing fluid through a multi-position directional valveincludes directing fluid through a nine-way, five-position pilotoperated directional spool valve.
 10. The method of claim 9, wherein thefirst actuator is a left actuator and the second actuator is a rightactuator, and wherein the nine-way, five-position pilot operateddirectional spool valve includes a right low power spool position, aright high power spool position, a no-flow spool position, a left lowpower spool position, and a left high power spool position, and whereinopening the main valve to a first position includes moving the spool toone of the right low power spool position and the left low power spoolposition.
 11. The method of claim 10, wherein opening the main valve toa second position includes moving the spool to one of the right highpower spool position and the left high power spool position.
 12. Themethod of claim 10, including biasing the nine-way, five-position pilotoperated directional spool valve to the no-flow position with at leastone spring.
 13. The method of claim 1, wherein operating the pilot valveto direct pilot fluid to a main valve in response to the first controlsignal includes providing pilot fluid to control movement of amulti-position directional valve to a low power position.
 14. The methodof claim 1, wherein operating the pilot valve to direct pilot fluid tothe main valve in response to the second control signal includesproviding pilot fluid to control movement of a multi-positiondirectional valve to a high power position.
 15. The method of claim 1,wherein operating the pilot valve to direct pilot fluid to a main valvein response to the first control signal and operating the pilot valve todirect pilot fluid to the main valve in response to the second controlsignal include operating a pilot valve of one of a primary steeringsystem and a redundant steering system.
 16. The method of claim 1,wherein the first actuator includes a first chamber and a secondchamber, and the second actuator includes a third chamber and a fourthchamber, and wherein directing fluid through the main valve to the firstactuator includes directing fluid to at least one of the first and thirdchambers.
 17. The method of claim 16, wherein directing fluid throughthe main valve to the first actuator includes directing fluid through alow power position of the main valve to the first chamber, and whereindirecting fluid through the main valve to the first actuator and thesecond actuator includes directing fluid through a high power positionof the main valve to the first chamber and the fourth chamber.
 18. Themethod of claim 1, wherein comparing the detected resistance to athreshold resistance includes comparing resistance detected by apressure sensor with a threshold value stored in a control module, andwherein opening the main valve to a second position includes shiftingthe main valve from a low power position to a high power position whenthe detected resistance exceeds the threshold value.
 19. A method ofoperating the hydraulic steering system of a machine, comprising:sending a first control signal from a control module to a pilot valve;operating the pilot valve to direct pilot fluid to a nine-way,five-position pilot operated directional spool valve in response to thefirst control signal; opening the nine-way, five-position pilot operateddirectional spool valve to a low pressure position in response to thepilot fluid; directing fluid through the nine-way, five-position pilotoperated directional spool valve to a head portion of a first actuator;detecting resistance to actuation of the first actuator; comparing thedetected resistance to a threshold resistance with the control module;sending a second control signal from the control module to the pilotvalve when the detected resistance exceeds the threshold resistance;operating the pilot valve to direct pilot fluid to the nine-way,five-position pilot operated directional spool valve in response to thesecond control signal; opening the nine-way, five-position pilotoperated directional spool valve to a high pressure position in responseto the pilot fluid; and directing fluid through the nine-way,five-position pilot operated directional spool valve to the head portionof the first actuator and a rod portion of a second actuator.
 20. Amethod steering a machine, comprising: sending a first control signalfrom a control module to a proportional solenoid steering pilot valve;operating the pilot valve to direct pilot fluid to a nine-way,five-position pilot operated directional spool valve in response to thefirst control signal; opening the nine-way, five-position pilot operateddirectional spool valve to a low pressure position in response to thepilot fluid; directing fluid through the nine-way, five-position pilotoperated directional spool valve to a first actuator; monitoring fluidpressure within the first actuator; comparing the monitored fluidpressure to a threshold value with the control module; sending a secondcontrol signal from the control module to the pilot valve when themonitored fluid pressure exceeds the threshold value; operating thepilot valve to increase the pilot fluid pressure to the nine-way,five-position pilot operated directional spool valve in response to thesecond control signal; opening the nine-way, five-position pilotoperated directional spool valve to a high pressure position in responseto the increased pilot fluid pressure; directing fluid through thenine-way, five-position pilot operated directional spool valve to boththe first actuator and a second actuator; continuing monitoring of fluidpressure within the first actuator; continuing comparing of themonitored fluid pressure to the threshold value; sending a changedcontrol signal from the control module to the pilot valve when themonitored fluid pressure falls below the threshold value; operating thepilot valve to decrease the pilot fluid pressure to the nine-way,five-position pilot operated directional spool valve in response to thechanged control signal; and opening the nine-way, five-position pilotoperated directional spool valve to a low pressure position in responseto the decreased pilot fluid pressure.